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A-B Editing

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A and B roll editing is a system of "checkerboard" editing used in the preparation of 16mm film and sometimes Super8 as well. The system came into use because of two problems with 16mm films. The first was that there existed no means of adding optical effects, such as fades and dissolves during the editing of the film. The other was that there was too little space between the frames of 16mm film for splices and the cuts encroached onto the frame making splices visible onscreen.

This is corrected by preparing two rolls of equal length in which successive scenes appeared on alternative rolls. The corresponding space on the other roll was filled with black leader which allowed a final copy with no visible splices. By printing the two rolls in succession on the same length of duplicating film, it is also possible to produce dissolves, fades and double exposures during the printing operation. The latter effects can only be done on printing machines that have automatic fading shutters but prints having only "invisible splices" can be made on any kind of printing machine.

A roll
A Roll B roll
B Roll

A process similar to A and B roll editing is used to mass produce film strips and slide sets. This technique is useful because a variety of original material is often necessary for the making of film strips and slide sets.

Both invisible splices and effects can, and usually are, included in the same set of A and B rolls. Furthermore, it is possible in special cases to prepare a third roll (C roll) containing scenes that are either too short to allow normal operation of the fading shutter in the printer or, more often, are carrying titles to be superimposed over certain scenes in the picture. The C roll must then be added to the process of combining the A and B rolls.

It is important to use the correct type of splicer for the A and B roll assembly. The ordinary "positive" splicer, which makes a splice that is symmetrical around the frame line won't work; the splices will always be visible. The correct type of splicer is the so-called "negative" splicer which makes a splice beginning at the frame line; width of the splice for this technique is immaterial.

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